Apparatus for coagulating treatment

ABSTRACT

An apparatus for coagulating treatment which is capable of controlling the amount of addition of a coagulant to the optimum level thereby minimizing the water content of the dehydrated cake comprises coagulant adding devices (6), (7), and (8) for causing the coagulant to be added in a variable amount to a liquid subjected to the coagulating treatment, a heat transfer detecting meter (12) disposed so as to contact the liquid to which the coagulant is to be added, the liquid to which the coagulant has been added, or the filtrate from the liquid to which the coagulant has been added and adapted to detect a feeble change in the physical property of the liquid in the form of a change in voltage, and a control device (16) for controlling the amount of addition of the coagulant in the coagulant adding device (8) so that the value of detection of the heat transfer detecting meter (12) is minimized or kept within a desired range.

FIELD OF THE INVENTION

This invention relates to an apparatus for coagulating treatment.Particularly, this invention relates to an apparatus for coagulatingtreatment aimed at controlling to optimize the amount of a coagulant tobe injected (added) to a liquid under treatment. More particularly, thisinvention relates to an apparatus for coagulating treatment suitable forcontrolling the amount of an organic coagulant (hereinafter referred tooccasionally as "polymer") to be added to a liquid under treatment.

BACKGROUND OF THE INVENTION

Heretofore, various methods have been proposed for the control of acoagulant to be added in the dehydration of sludge. It has beenproposed, for example, to control the amount of a coagulant to be addedby indirectly measuring the residual polymer content of the liquid withthe aid of a viscosimeter in view of the fact that the viscosity of theliquid varies with the residual polymer content and then using theresult of this measurement as the criterion for the control.

The physical properties of the liquid include specific heat, electricconductivity, etc. besides the viscosity. They bring about variouseffects on the operation of addition of the coagulant. When the amountof addition of the coagulant is controlled by using as a sole criterionthe viscosity which is only one of the physical properties, therefore,the actual amount of addition deviates from the proper level possibly tothe extent of entailing ineffective coagulation, excessive addition ofthe coagulant, and unduly high cost of the coagulant.

DISCLOSURE OF THE INVENTION

An object of this invention is to solve the problems of the prior artdescribed above and provide an apparatus for the coagulating treatmentwhich allows the amount of addition of a coagulant to be controlledaccurately and consequently optimized.

Another object of this invention is to provide a coagulating treatmentapparatus which prevents the amount of addition of a coagulant fromotherwise possibly deviating and accomplishes the coagulating treatmentinexpensively and efficiently.

These objects are accomplished by an apparatus for the coagulatingtreatment wherein a coagulant is added to a liquid subjected to thecoagulating treatment, which apparatus comprises a device for coagulantaddition capable of adjusting the amount of addition of the coagulant, aliquid to which the coagulant is to be added, a heat transfer detectordisposed so as to contact the liquid containing the added coagulant orthe filtrate from the liquid containing the added coagulant, and acontrol device for controlling the amount of the coagulant supplied bythe device for coagulant addition in accordance with the value ofdetection displayed on the heat transfer detector.

The present invention resides in controlling the amount of addition of acoagulant to a sludge by detecting changes in the physical constants ofthe sludge due to changes in the properties of the sludge as changes inheat transfer and adopting the detected changes in heat transfer as thecriterion for the control.

The inventors made a study for many years concerning the dehydratingproperty of a liquid resulting from a coagulating treatment, to acquirea knowledge that the water content of the cake resulting from thedehydration, the detected value with the heat transfer detector in theliquid produced by the coagulating treatment (or the liquid undergoingthe coagulating treatment) and the concentration of added coagulant inthe sludge are closely relates to each other as illustrated in FIGS. 5and 6, and the water content of the dehydrated cake is minimized bycontrolling the amount of addition of the coagulant so as to minimizethe numerical value detected by the use of a hot-wire current meter, forexample, in addition to the conventional knowledge.

FIGS. 5 and 6 are graphs showing the relation among the amount ofaddition of a coagulant (cationic polymer) to a sewage-mixed raw sludgeas a raw water, the value of detection (potential difference) indicatedon a hot-wire flow meter, and the water content of dehydrated cake.

As shown in FIG. 5, the value of detection indicated by the hot-wirecurrent meter is in the minimum zone and the water content of thedehydrated cake is minimum when the amount of addition of the coagulantis about from 150 to 200 ppm.

FIG. 6 is a diagram showing a similar relation obtained of a differentmixed raw sludge from the sludge of FIG. 5. It is seen that the value ofdetection indicated by the hot-wire current meter and the water contentof the dehydrated cake are both minimum when the amount of addition of acoagulant was approximately in the neighborhood of 150 ppm. When thistest was repeated on various kinds of raw waters, the results clearlyshowed relations similar to those shown in FIGS. 5 and 6. It has beenfurther demonstrated that relations similar to those mentioned aboveexist concerning properties of cake separation and amount of filtratebesides the water content of the cake.

The present invention has been completed on the basis of theseknowledges. Since it effects the control of the amount of addition of acoagulant based on the value of detection obtained with a heat transferdetector, it is capable of adjusting the amount of addition of thecoagulant so as to minimize the water content of the dehydrated cake.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, FIG. 2, and FIG. 3 are system diagrams of an apparatus embodyingthe present invention.

FIG. 4 is a block diagram of a hot-wire current meter.

FIG. 5 and FIG. 6 are graphs showing test results.

FIG. 7A and FIG. 7B are graphs to aid in the explanation of the methodof control.

FIG. 8 is a system diagram of another apparatus embodying the presentinvention.

FIG. 9 is a partial structural diagram.

FIG. 10 is a system diagram of yet another apparatus embodying thepresent invention.

FIG. 11 is a partial structural diagram of the XI part of FIG. 10.

FIG. 12 and FIG. 13 are system diagrams of still another apparatusembodying the present invention.

BEST MODE OF EMBODYING THE INVENTION

Now, the present invention will be described below with reference toworking examples as illustrated in the accompanying drawings.

FIG. 1 is a system diagram of an apparatus for the coagulating treatmentin one working example of this invention. The raw water from a rawsludge pit 1 is forwarded through a pipe 3 provided with a pump 2 andintroduced into a coagulation tank 4. The coagulation tank 4 is providedwith a stirrer 5 and is supplied with a cationic organic coagulant froma coagulant injecting device which comprises a coagulant storage tank 6,a coagulant injection pipe 7, and a coagulant injection pump 8. Theliquid resulting from the coagulating treatment in the coagulation tank4 is transferred to a dehydrator 9 as solid-liquid separating means. Thedehydrated cake produced in the dehydrator 9 is forwarded to the step ofcake disposal using an incinerator, for example, while the filtrate isforwarded to a filtrate storage tank 10.

The filtrate storage tank 10 is provided with a thermometer 11, a heattransfer detector 12, and an electric conduction meter 13.

The detection signals issued from these measuring instruments 11, 12,and 13 are introduced into an operation controller 16. The operationcontroller 16 system diagrams a control signal to the coagulantinjection pump 8. The pump 8 is subjected to inverter control, forexample.

As the heat transfer detector contemplated by this invention, a hot-wiretype or hot-film type current meter or a heat conductivity meter whichis generally used for the detection of heat transfer can be adopted.

Otherwise, a device which is provided with a self-heating source capableof energizing a heater and effecting required heating or a device whichis provided with a heating source such as the combination of a heaterwith a thermometer and, is allowed to effect indirect heating with theheater, may be adopted.

Now, the present invention will be described below with reference to anembodiment resorting to a hot-wire current meter.

The hot-wire current meter, as universally known, is designed to keep aflow of a fixed electric current to a hot wire serving as a heatingmember and insert this hot wire in a fluid. A change in the flow rate ofthis fluid produces a proportionate change in the degree with which thefluid deprives the hot wire of heat. As a result, the temperature of thehot wire is changed and the resistance thereof is also changed. Thehot-wire current meter detects this change in resistance in the form ofa change in voltage and determines the flow rate of the fluid.

The present invention utilizes the operating principle of this hot-wirecurrent meter, sets conditions for a constant flow rate of the fluidand, thereby, determines a change in the flow rate by detecting thetransfer of feeble heat removed from the hot wire in the form of achange in resistance (voltage) and then perceiving this change inresistance in the form of a change in physical property. The filtratestorage tank 10, therefore, is provided with a stirrer 14 and, for thepurpose of enabling the stirrer 14 to be rotated constantly at a fixedspeed in the course of measurement and, at the same time, uniformizingthe conditions of stirring, further provided with an overflow pipe 15adapted to maintain a fixed level in the tank.

FIG. 4 is a schematic structural diagram of the hot-wire current meter12 which is used in the present working example. This hot-wire currentmeter 12 is provided with a hot wire (resistor) 12a, constant-currentgenerator 12b, and a voltmeter 12c.

The hot wire 12a is kept in contact with the liquid being circulated ata fixed flow rate as indicated by an arrow mark S inside the filtratestorage tank 10. While this liquid has fixed physical properties, thehot wire 12a in which a constant current is flowing offers a fixedresistance and consequently a constant voltage because the amount ofheat removed from the hot wire 12a is fixed. When a change occurs in thephysical properties of the liquid, the resistance is varied because theamount of heat removed from the hot wire 12a is varied. To be specific,the change in resistance occurs because there arises transfer of heatfrom the hot wire into the liquid. Since the electric current flowing inthe hot wire 12a is constant, the change in resistance can be detectedas a change in voltage. This change in voltage represents the detectedvalue of the physical property in the liquid. The change in the physicalproperty of the hot wire 12a may be detected in the form of a change inresistance or in voltage.

The working example has been described as using a constant-currenthot-wire current meter. Optionally, this invention may be embodied witha constant-temperature type hot-wire current meter.

As clearly noted from the description made thus far, the use of thehot-wire current meter in the way contemplated by this invention permitsdetection of even a feeble change in physical property by simply givinga fixed flow rate.

In the apparatus of FIG. 1 which is constructed as described above, theraw water in the coagulation tank 4 is subjected to a coagulatingtreatment caused by addition of a coagulant. The amount of addition ofthis coagulant in this case is so controlled as to minimize the value ofthe detection made in the filtrate storage tank 10 and indicated by thehot-wire current meter.

The method for controlling the amount of addition of the coagulant willbe described below with reference to FIG. 7A and FIG. 7B. FIG. 7A andFIG. 7B are typical diagrams intended to aid in the explanation. Whilethey show changes, Δn, in the amount of addition of a coagulant withgreat exaggeration, the actual changes may be properly selected to suitthe kind of polymer, for example.

With reference to FIG. 7A, it is assumed that the amount of addition ofa coagulant at a given time t₁ is n₁ and the amount of addition of thecoagulant at the next time t₂ is n₂ (n₂ is a feeble amount, Δn, largerthan n₁. When the values of detection, a₁ and a₂, of the hot-wirecurrent meter obtained respectively for the amounts, n₁ and n₂, ofaddition are compared and a₂ is found to be smaller than a₁, the amountof addition at the subsequent time t₃ is changed to n₃ (n₃ is Δn largerthan n₂). This procedure is repeated. As a result, the amount ofaddition is gradually approximated to the amount of addition, N, thatminimizes the value of detection of the hot-wire current meter.

With reference to FIG. 7B, the value of detection of the hot-wirecurrent meter grows from a₁ to a₂ as the amount of addition is increasedfrom n₁ to n₂. In this case, the amount of addition at the subsequenttime t₃ is decreased from n₂ to n₃ (n₃ is Δn smaller than n₂). Then, atthe further subsequent time t₄, the amount of addition is changed to n₄(n₄ is Δn smaller than n₃). By repeating this procedure, requiredapproximation to the amount of addition, N, that minimizes the value ofdetection of the hot-wire current meter can be attained.

With reference to FIG. 7A and FIG. 7B, the repeated change in the amountof addition by a fixed increment Δn may possibly result in an excessamount beyond the optimum amount of addition N. If this excess additiontakes place, the amount of addition is decreased by 1/2Δn at a time, forexample. When the repeated decrease in the amount of addition results inan excess amount beyond the optimum amount N, then the amount ofaddition is reversively returned by 1/4Δn. By gradually decreasing therate of decrement in the manner just mentioned, the amount of additioncan be eventually brought to coincidence with the maximum amount ofaddition N.

Even after the optimum amount of addition N is reached, there stillexists the possibility of change of the optimum amount of addition Nitself, so that it is desirable to keep the amount of addition varied ata prescribed rate even after it has reached the optimum amount. As aresult, it is possible to vary quickly to follow a possible change inthe optimum amount.

In the apparatus illustrated in FIG. 1, the values of detection of thethermometer 11 and the electric conductivity meter 13 are alsointroduced into the operation controller 16. This is because the valueof detection of the hot-wire current meter 12 is affected by a possiblechange in the attributes of the raw water (such as temperature andsoluble salt concentration) and, therefore, the portions of contributionmade by the changes in temperature and electric conductivity to thechange in the value of detection of the hot-wire current meter must bewithdrawn (compensated) to allow sole comparison of changes in the valueof detection of the hot-wire current meter exclusively with respect tochanges in the amount of addition.

FIG. 2 is a system diagram of an apparatus for coagulating treatment asanother embodiment of the present invention.

In this embodiment, a first and a second coagulation tank 41, 42 areinstalled. To the first coagulation tank 41, a cationic polymer from itsstorage tank 61 is added via a coagulant injection pipe 71 and acoagulant injection pump 81. To the second coagulation tank 42, ananionic polymer from its storage tank 62 is supplied via a coagulantinjection pipe 72 and a coagulant injection pump 82.

To the coagulation tanks 41, 42, filtering devices 101, 102 assolid-liquid separating means are respectively connected via dischargepipes 91, 92 adapted to release liquids from the tanks. The filtratesemanating from these filtering devices are stored respectively infiltrate storage tanks 111, 112. The filtrate storage tanks 111, 112 areprovided with the thermometers 11, the hot-wire current meters 12, andthe electric conductivity meters 13. The detection signals from thesemeasuring instruments are introduced into the operation controller 16.The coagulant injection pump 81 is controlled in accordance with thedata of detection from the filtrate storage tank 111 and the coagulantinjection pump 82 is controlled in accordance with the data of detectionfrom the filtrate storage tank 112. This method of control is identicalwith that which has been described with reference to the apparatus ofFIG. 1.

Also in the apparatus of FIG. 2, the coagulant injection pumps 81, 82may be controlled based on the values of detection of the hot-wirecurrent meter, the temperature, and the electric conductivity obtainedthrough the filtrate from the dehydrator 9.

In the apparatus of FIG. 2, the detection with the hot-wire currentmeter is effected on both the liquids in the two coagulation tanks 41,42. Optionally, the detection with the hot-wire current meter may beeffected on the liquid in the first coagulation tank 41 and the controlmentioned above may be effected only with respect to the amount ofaddition of the cationic polymer. In this case, the amount of additionof the anionic polymer may be proportionated to the controlled amount ofaddition of the cationic polymer. Since the sludge is negativelycharged, the control is made nearly perfectly by using as the maintarget of control the amount of addition of the cation polymer which isadded first.

FIG. 3 is a system diagram of an apparatus for coagulating treatment asstill another embodiment of this invention.

In this embodiment, an inorganic coagulant is added to the firstcoagulation tank 41 and an amphoteric polymer is added to the secondcoagulation tank 42. The detection with the hot-wire current meter iseffected on the filtrate from the second coagulation tank 42 and theamounts of addition of the polymers are controlled in accordance withthe aforementioned procedure using the results of the detection. In thiscase, the outcome of the detection with the electric conductivity meterdisposed in the filtrate storage tank 112 is used for the purpose ofcompensating for the effect of the addition of the inorganic coagulant.

Again in the present embodiment, the detection with the hot-wire currentmeter may be effected on the filtrate from the dehydrator 9 and thecontrol of the amount of addition may be effected on the basis of theoutcome of the detection in the same manner as in the embodiment of FIG.1.

In the present embodiment, the detection with the hot-wire current meteris not effected on the liquid held in the first coagulation tank 41.This is because no clear discrimination may be made as to the questionwhether changes in the value of detection with the hot-wire currentmeter with respect to the liquid held inside the second coagulation tank42 are ascribable to the influence of the inorganic coagulant or to thatof the polymer if the filtrate from the first coagulation tank 41 isadditionally subjected to detection and control.

In the embodiment of FIG. 3, the first coagulation tank 41 is providedwith a pH meter 30 and the amount of addition of the inorganic coagulantis controlled based on the pH data produced by the pH meter so as to beapproximated to the optimum amount of addition. In consequence of thiscontrol, the otherwise possible excessive addition of the inorganiccoagulant is precluded, the effect of the inorganic coagulant on thevalue of detection of the hot-wire current meter is alleviated to agreat extent, and the accuracy of the control of the amounts of additionof the polymers is enhanced.

Particularly when the amphoteric polymer is used as in the presentembodiment, the control by means of the pH meter 30 proves to bedesirable in the sense of curbing the elution of cation or anion.

In the apparatuses of FIGS. 1 to 3, the coagulated sludge may be evenpelletized within the tank by controlling the amount of addition and therevolution number of the stirrer in the coagulation tank.

In the present invention, the hot-wire current meter alone may be usedand the thermometer and other measuring instruments may be omitted.Further, the embodiment of FIG. 1, similarly to the apparatuses of FIGS.2 and 3, may be operated so as to effect the detection with the hot-wirecurrent meter on the liquid held in the coagulation tank.

Though the present embodiment is depicted as adding the coagulant to thecoagulation tank, the present invention may be alternatively embodied inan apparatus of coagulating treatment of the type allowing the coagulantto be injected into a pipe for the liquid subjected to the coagulatingtreatment (the feed pipe for the raw water, for example).

FIG. 8 is a system diagram of an apparatus for the coagulating treatmentconforming to this type of embodiment. The raw water from a raw waterstorage tank is forwarded via a pipe 201 provided with a raw water pump(not shown) to a centrifugal dehydrator (which may be a belt pressdehydrator or a screw press dehydrator; the type of dehydratorirrelevant) 203.

To an inlet halfway along the length of the raw water pump-incorporatingpipe 201, a cationic organic coagulant from a coagulant injection deviceprovided with a coagulant injection pipe 202 and a coagulant injectionpump 207 is supplied. The solid residue emanating from the dehydrator203 is discharged through a concentrated sludge outlet 204, to bedisposed of separately. The relatively clean liquid separated by thedehydrator is forwarded via a separated clean liquid outlet 205 to aseparated liquid storage tank 208. A part of the separated liquidcollected in the separated liquid storage tank 208 is quantitativelyforwarded by a pump 209 to a sampling tank 215. This sampling tank 215is provided with a heat transfer meter (hot-wire current meter) 210.

The heat transfer meter of this kind is susceptible conspicuously of theinfluence of the flow speed of the liquid or susceptible of theinfluence of the pulsation of the transfer pump 209. To eliminate theseinfluences, the present embodiment is adapted to give to the heattransfer meter a relatively large fixed flow by the use of a stirringdevice 214 so as to render a possible change in flow volume negligible.When the separated water is caused to flow into the sampling tank byvirtue of the difference of height of water level, the pump 209 isomitted as illustrated in FIG. 9 which is a system diagram illustratinganother structure for the IX part shown in FIG. 8. Conversely, when thepump 209 is of the type capable of discharging a given fluidcontinuously at a constant flow rate, the stirring device 214 may beomitted.

In the sampling tank 215, the condition, i.e. physical property, of theseparated water is determined with the heat transfer meter 210. Thesignal of detection from the heat transfer meter 210 is forwarded to asignal amplifier-converter 211 to be converted into the form fit for theoperation in the operation controller therein. An operation controller212, in response to the signal from the converter 211, issues a statedoperation signal to the drive device for the coagulant injection pump207 and consequently effects the control of the amount of addition ofthe coagulant from the coagulant injection pump 207 through thecoagulant injection pipe 202. Preferably, the drive device for thecoagulant injection pump 207 is of the type capable of continuouslyvarying the amount of discharge of the pump, i.e. amount of addition ofthe coagulant, as an inverter.

In FIGS. 8 and 9, each of the reference numerals 213a, 213b denotes anoutlet pipe for the treated liquid.

FIG. 10 is a system diagram of an apparatus embodying the presentinvention by the combined use of an organic coagulant (amphotericpolymer) and an inorganic coagulant. In the present embodiment, theinorganic coagulant is injected into the raw water pipe 201 by acoagulant injection pump 250, and the organic coagulant is subsequentlyinjected into the pipe 201. Between the points of addition of theinorganic coagulant and the organic coagulant, a sensor 251 such as, forexample, a pH meter or an electric conductivity meter is provided. Onthe basis of the signal of detection from this sensor 251, a controller252 effects the control of the injection of the inorganic coagulant. Theremainder of the construction of this embodiment is identical to theconstruction of the embodiment of FIG. 8. Thus, like component parts aredenoted by like reference numerals. Also in this embodiment, theinjection pump 207 for the organic coagulant is controlled based on thedetection signal from the heat transfer meter 210.

The apparatus of FIG. 10 may be provided, as illustrated in FIG. 11illustrating another construction for the XI part shown in FIG. 10, witha sensor 255 for measuring the pH value or electric conductivity of theseparated water. The control of the addition of the coagulant,accordingly, may be effected on the basis of the detection signal fromthis sensor 255. Optionally, this embodiment may be further providedwith a thermometer. It is also permissible to have the separated waterstorage tank and the sampling tank integrally formed as illustrated inFIG. 11.

Though the embodiments cited thus far invariably cause the filtrate toflow continuously into the filtrate storage tank, the present inventionmay otherwise cause the filtrate to be received portionwise in a statedamount into the filtrate storage tank and the detection with thehot-wire current meter may be effected on the separate portions of thefiltrate. The batchwise determination involved in this case can beattained by having a level gauge provided for the filtrate storage tankand operating this level gauge in allowing a new batch of the filtrateto flow continuously into the tank completely evacuated of the previousbatch of the filtrate until it reaches the stated level and subsequentlysetting the hot-wire current meter to service.

The present invention may omit the thermometer and rely solely on thehot-wire current meter. It is also allowed to effect the control of theamount of addition by using the cake separation or the amount offiltrate as the criterion of control instead of the water content of thedehydrated cake. It may use two or more of these characteristicproperties as criteria for the control of the amount of addition of acoagulant.

In the embodiments cited above, the filtrate resulting from thedehydration of the coagulant-added liquid is held in contact with thehot-wire current meter. This arrangement is effective in preventing theSS component and the floc from adhering to the hot-wire current meter,stabilizing the operation of the apparatus, and facilitating themaintenance of the apparatus. Optionally, the present invention allows amodification such that the hot-wire current meter directly contacts theliquid before the addition of a coagulant or the liquid before thecoagulating treatment as illustrated in FIG. 12 and FIG. 13. Each of theapparatus of FIG. 12 and FIG. 13 is provided with a storage tank 10A foradmitting the liquid before the addition of a coagulant (FIG. 12) or theliquid before the coagulating treatment (FIG. 13) in place of thefiltrate storage tank 10. The remainders of the construction of theapparatuses of FIG. 12 and FIG. 13 are identical with the constructionof the apparatus of FIG. 1. Thus, like component parts are denoted bylike reference numerals.

The expression "filtrate from the coagulant-added liquid" as used in thepresent invention means the filtrate resulting from the filtration ofthe liquid in the coagulation tank and the dehydrated filtrate resultingfrom the dehydration of the filtrate just mentioned with the dehydrator.

In the data of control illustrated in FIG. 7, the control is carried outso as to minimize the amount of addition of a coagulant. Optionally, thecontrol may be performed so that the amount of addition of a coagulantwill fall in a target range.

Economic Utility of the Invention

As described above, the apparatus of this invention for the coagulatingtreatment, owing to the use of a heat transfer meter, is capable ofeasily detecting a feeble change in the physical property of a givenliquid in the form of a change in resistance (voltage) and consequentlyeffecting accurate control of the amount of addition of a coagulant andensuring desired optimization of the amount of addition of thecoagulant. Thus, the otherwise possible deviation of the amount ofaddition of the coagulant is avoided and the required coagulatingtreatment is effectively and inexpensively carried out.

We claim:
 1. An apparatus for effecting coagulation by addition of acoagulant to a liquid, comprisinga coagulant adding device capable ofadjusting an amount of addition of the coagulant, means for receivingthe coagulant from the coagulant adding device and for effectingcoagulation with the liquid, means for separating a coagulated materialinto a solid content and a liquid content, heat transfer detecting meterso disposed as to contact with one of the liquid to which the coagulantis to be added, the coagulated material before separation and the liquidcontent separated by said separating means, and a control devicecommunicating with the heat transfer detecting meter and the coagulantadding device for controlling an amount of addition of the coagulant inthe coagulant adding device, said amount of the coagulant to be added insaid coagulant adding device being controlled by said control devicebased on an outcome detected by said heat transfer detecting meter.
 2. Acoagulating apparatus for effecting coagulation in a liquid by additionof a coagulant, comprising first guiding means for receiving a liquid tobe subjected to a coagulating treatment and guiding the received liquidto at least one part at which the coagulant is added, adding means foradding the coagulant to the liquid in a variable amount at the part foraddition of the coagulant, solid-liquid separating means for separatingthe liquid with the coagulant into a liquid content and a solid content,second guiding means situated between the adding means and theseparating means to guide the liquid to the separating means, a heattransfer detecting meter disposed so as to contact the liquid contentseparated by the solid-liquid separating means, and control means forcontrolling an amount of addition of the coagulant through the addingmeans so that a value of detection of the heat transfer detecting meteris minimized to be within a target range.
 3. An apparatus set forth inclaim 2, wherein the adding means is a coagulation tank provided withstirring means.
 4. An apparatus set forth in claim 3, wherein saidsolid-liquid separating means separates a part of a liquid in thecoagulation tank into the liquid content and the solid content, theseparated liquid content is caused to contact the heat transferdetecting meter, and a remaining part of the liquid in the coagulationtank is delivered separately to the downstream side of the guidingmeans.
 5. An apparatus set forth in claim 2, wherein the solid-liquidseparating means is a dehydrator.
 6. An apparatus set forth in claim 2,wherein the solid-liquid separating means is a filtrating device.
 7. Anapparatus set forth in claim 2, wherein said adding means includes aplurality of parts for addition of the coagulant.
 8. An apparatus setforth in claim 7, wherein said plurality of parts comprises a first partused for addition of a cationic coagulant and a second part used foraddition of an anionic polymer coagulant.
 9. An apparatus set forth inclaim 7, wherein said plurality of parts comprises a first part used foraddition of an inorganic coagulant and a second part used for additionof a polymer coagulant.
 10. An apparatus set forth in claim 9, whereinsaid control means controls an amount of addition of the polymercoagulant alone.
 11. An apparatus set forth in claim 10, wherein saidcontrol means controls an amount of addition of the inorganic coagulanton the basis of one of a pH value or an electric conductivity of aliquid to which the inorganic coagulant has been added.
 12. An apparatusset forth in claim 2, wherein said first guiding means is a pipe forpassing the liquid for treatment and said adding means is a feed pipeconnected to the pipe and adapted to supply the coagulant to the pipe.13. An apparatus set forth in claim 12, wherein the solid-liquidseparating means is a centrifugal dehydrator.
 14. An apparatus set forthin claim 2, wherein said heat transfer detecting meter is also coupledto one of a thermometer or an electric conductivity meter, disposed soas to contact the liquid content separated by the solid-liquidseparating means so that the control means is enabled to effect requiredcompensation on the basis of the value of detection of the detectingmeans.
 15. An apparatus set forth in claim 2, wherein the heat transfermeter is one of a hot-wire current meter and a hot-film type currentmeter.
 16. An apparatus set forth in claim 2, wherein the adding meansincludes a tank for a liquid of the coagulant, and a pump and a pipe forforwarding the liquid in the tank to the part.